Ocean Frontal Effects on the Vertical Development of Clouds over the Western North Pacific: In Situ and Satellite Observations*

Abstract

A suite of shipboard and satellite observations are analyzed and synthesized to investigate the threedimensional structure of clouds and influences from sea surface temperature fronts over the western North Pacific. Sharp transitions are observed across the Kuroshio Extension (KE) front in the marine atmospheric boundary layer (MABL) and its clouds. The ocean's influence appears to extend beyond the MABL, with higher cloud tops in altitude along the KE front than the surroundings.In winter, intense turbulent heat release from the ocean takes place on the southern flank of the KE front, where the cloud top penetrates above the MABL and reaches the midtroposphere. In this band of high cloud tops, frequent lightning activity is observed. The results of this study suggest a sea level pressure mechanism for which the temperature gradient in the MABL induces strong surface wind convergence on the southern flank of the KE front, deepening the clouds there.In early summer, sea fog frequently occurs on the northern flank of the subtropical KE and subarctic fronts under southerly warm advection that suppresses surface heat flux and stabilizes the surface atmosphere. Sea fog is infrequently observed over the KE front even under southerly conditions, as the warm ocean current weakens atmospheric stratification and promotes vertical mixing. The KE front produces a narrow band of surface wind convergence, helping support a broad band of upward motion at 700 hPa that is associated with the eastward extension of the baiu rainband from Japan in June-July.

Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

“…During winter, when cold and dry air from the Asian landmass blows over the warm KE water, extremely large amounts of heat are released to the atmosphere by the ocean. This heating can warm and destabilize the atmospheric boundary layer, affecting the clouds (Tokinaga et al, 2009) and surface winds (Nonaka and Xie, 2003). Differential heating associated with the KE's Sea Surface Temperature (SST) front can cause surface wind convergence and a secondary circulation within the troposphere (Minobe et al, 2008;Tokinaga et al, 2009), as well as enhanced baroclinicity that can affect the storm track (Taguchi et al, 2009).…”

“Hot Spots” in the climate system—new developments in the extratropical ocean–atmosphere interaction research: a short review and an introduction

“…A frontal SST gradient also yields surface convergence/divergence through enhanced (suppressed) heat release from the ocean on the warmer (cooler) side of the front that hydrostatically acts to lower (raise) surface pressure and resultant frictional convergence (divergence) (Shimada and Minobe 2011;Tanimoto et al 2011). Generated through this pressure adjustment mechanism or the vertical momentum mixing mechanism (Schneider and Qiu 2015), the surface convergence yields ascending motion at the top of the boundary layer, acting to enhance cloudiness and precipitation locally (Tokinaga et al 2009;Tanimoto et al 2011;Masunaga et al 2015). Through essentially the same mechanisms, meso-scale oceanic eddies can also leave meso-scale imprints on surface wind, cloudiness and precipitation patterns.…”

Turbulent heat fluxes during an intense cold-air outbreak over the Kuroshio Extension Region: results from a high-resolution coupled atmosphere–ocean model

“…Recent discussions are given by , Small et al (2008), Taguchi et al (2009), andTokinaga et al (2009).…”

“…From 2 February until the end of the simulation, maximum heat fluxes are found in the areas where two meanders of warm subtropical water protrudes to the north and on the south side of the Kuroshio front. The southern flank of the Kuroshio was also indentified as the location of intense sensible and latent heat fluxes in the study of Tokinaga et al (2009). The variation in heat flux is primarily due to changes in wind speed (Fig.…”